1. Field of the Invention
The present invention relates to an image forming. apparatus having a fixing device for fixing a developer image on a recording medium by means of self-heating of a heating member based on loss of an eddy current caused in the heating member by applying a radio-frequency magnetic field generated by a coil to the heating member.
2. Description of the Related Art
In an image forming apparatus using digital technology, generally known as an electronic copying machine, an original table on which an original is placed is exposed. An image signal corresponding to a reflection light amount from the original table is obtained from a CCD (charge-coupled device) line sensor. A laser beam corresponding to the image signal obtained from the line sensor is radiated on a photosensitive drum, and thus an electrostatic latent image is formed on a peripheral surface of the photosensitive drum. The electrostatic latent image is changed to a visible image by adherence of a developer (toner) which is (negatively) charged in advance. A paper sheet is fed to the photosensitive drum in accordance with the timing of rotation of the photosensitive drum, and the visible image (developer image) on the photosensitive drum is transferred onto the paper sheet. The paper sheet with the transferred developer image is fed to a fixing device.
The fixing device comprises a heating roller and a pressing roller put in pressure contact with the heating roller. The paper sheet is inserted between both rollers, and while the sheet is being conveyed, the developer image on the sheet is fixed by the heat of the heating roller.
An example of a heat source for the heating roller is an induction heater. The induction heater comprises a coil contained within the heating roller, and a radio-frequency generating circuit for supplying a radio-frequency current to the coil.
The radio-frequency generating circuit comprises a rectifier circuit for rectifying an AC power supply voltage, and a switching circuit for converting an output voltage (DC voltage) of the rectifier circuit to a radio-frequency power with a predetermined frequency. The coil is connected to an output terminal of the radio-frequency generating circuit (an output terminal of the switching circuit).
When the radio-frequency generating circuit is operated, a radio-frequency current is supplied to the coil, and the coil generates a radio-frequency magnetic field. The radio-frequency magnetic field is applied to the heating roller, and an eddy current is produced in the heating roller. The heating roller emits heat by itself based on a loss of the eddy current, and the developer image on the paper sheet is fixed by the heat.
In the case of the fixing device using the above-described induction heater, there are such error statuses as IGBT abnormality, voltage abnormality, circuit failure, and coil breakage.
In the case of the fixing device using the induction heater, however, the range of a voltage margin of an induction heater unit side circuit is narrower than that of a voltage margin of the image forming apparatus body. Thus, compared to a case where a conventional heater is used, the frequency of error statuses relating to voltage variations increases and the control may be disabled.
The present invention has been made in consideration of the above circumstances, and the object of the invention is to avoid a control-disabled state by properly coping with an error status in accordance with a voltage variation.
The present invention provides an image forming apparatus for forming an image, including a fixing device having a coil in a heating roller and causing the coil to generate a radio-frequency magnetic field, thereby producing an eddy current in the heating roller and fixing a developer image on a recording medium by means of self-heating of the heating roller based on an eddy current loss, the apparatus comprising: receiving means for receiving a voltage abnormality error signal from the fixing device; time-measuring means for measuring a reception time of the voltage abnormality error signal when the receiving means has received the voltage abnormality error signal; confirmation means for confirming whether the reception time measured by the time-measuring means exceeds a predetermined limit value; first control means for executing a control to ignore the voltage abnormality when the conformation means has confirmed that the limit value is not exceeded; and second control means for executing a control to perform an error process for the occurrence of voltage abnormality, when the confirmation means has confirmed that the limit value is exceeded.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.